System and method for providing simultaneous multiple push-to-talk over cellular multimedia service

ABSTRACT

A system and method provide simultaneous multiple push-to-talk (PTT) over cellular (PoC) multimedia service, and enable a PoC client performing an OMA PoC multimedia communication service to be simultaneously provided with a plurality of media streams, and also allows efficient media transmission through media adaptation adjusting capacity of each of the media streams provided at the same time.

CLAIM OF PRIORITY

This application claims the benefit under 35 U.S.C. §119(a) from anapplication entitled “SYSTEM AND METHOD FOR PROVIDING SIMULTANEOUSMULTIPLE PUSH-TO-TALK OVER CELLULAR MULTIMEDIA SERVICE” filed in theKorean Intellectual Property Office on Sep. 30, 2005 and assigned SerialNo. 2005-92256, the entire contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a system and method for providingsimultaneous multiple push-to-talk (PTT) over cellular (PoC) multimediaservice.

2. Description of the Related Art

Significant developments in mobile communications technology and theextension of mobile communications networks have resulted in thedevelopment of a vast array of services and applications for use with acellular phone.

Concurrently, there is an increasing demand from cellular phone usersfor additional services, such as a location, a multimedia, and apush-to-talk (PTT) service. Among these additional services, the PTTservice supports various supplementary functions such as an instantmessenger function and a status display, as well as a group call and avoice call which are also provided by an existing radio or a trunk radiosystem (TRS).

Currently, standardization of a PoC service which utilizes the PTTfunction in a mobile communication network is actively proceeding. Oneunique feature of the PoC service that differs from existing mobilecommunication services is that a user can participate in a plurality ofPoC sessions, and so can use a call service while moving among the PoCsessions as needed. A requirement that the user should be able to usethe call service while moving among the plurality of PoC sessions isspecified in the Open Mobile Alliance (OMA), which is a forum forspecifying mobile communications services.

Meanwhile, a current PoC system supports a multimedia communicationservice. To this end, the PoC system defines video, images, text, voice,etc. as a new type of multimedia. Further, the current PoC system candisplay a multistream (e.g. video or images) owing to improvedperformance of terminals.

However, the current PoC system is not capable of simultaneouslytransmitting a plurality of multimedia streams to a terminal during amultisession.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a system and methodthat provide simultaneous multiple push-to-talk (PTT) over cellular(PoC) multimedia service in a PoC system, capable of simultaneouslytransmitting a plurality of media streams to a PoC terminal during amultisession.

Another object of the present invention is to provide a system andmethod that provide simultaneous multiple push-to-talk (PTT) overcellular (PoC) multimedia service, capable of providing traffic controlconsidering a capacity of a wireless network or system performance whena plurality of media streams are simultaneously transmitted to a PoCterminal during a multisession.

The present invention provides a method and system for making itpossible to efficiently transmit media in consideration of features ofthe media so that a PoC client performing OMA PoC multimediacommunication service simultaneously receives and displays visual mediasuch as images and video.

According to the present invention, there is provided a method forproviding simultaneous multiple push-to-talk-over-cellular (PoC)multimedia service in a PoC system. The method includes receiving arequest for establishment of a new PoC multimedia session of a PoCterminal performing multimedia PoC service through a pre-established PoCsession; checking whether the PoC terminal supports simultaneousmultiple multimedia sessions and whether the PoC terminal requests mediaadaptation; adjusting sizes of multimedia data being transmitted anddata to be transmitted to the PoC terminal according to whether the PoCterminal supports simultaneous multiple multimedia sessions and whetherthe PoC terminal requests media adaptation; and transmitting theadjusted data to the PoC terminal.

The step of checking whether the PoC terminal supports simultaneousmultiple multimedia sessions and whether the PoC terminal requests mediaadaptation may includes checking whether an auto-answer mode of the PoCterminal is set up; and detecting pre-stored setup information about thePoC terminal when the auto-answer mode is set up, and checking whetherthe PoC terminal supports simultaneous multiple multimedia sessions andwhether the PoC terminal requests media adaptation.

Also, the step of checking whether the PoC terminal supportssimultaneous multiple multimedia sessions and whether the PoC terminalrequests media adaptation may include transmitting a message queryingwhether the PoC terminal supports simultaneous multiple multimediasessions and whether the PoC terminal requests media adaptation; andreceiving a response message to the query message from the PoC terminal,detecting information included in the response message, and checkingwhether the PoC terminal supports simultaneous multiple multimediasessions and whether the PoC terminal requests media adaptation.

According to another aspect of the present invention, there is provideda message used for providing simultaneous multiplepush-to-talk-over-cellular (PoC) multimedia service. The messageincludes a Session Initiation Protocol (SIP) message having Talk BurstControl Protocol (TBCP) option parameters indicating whether mediaadaptation is requested, whether an uplink or downlink exists, and atype of media data.

According to yet another aspect of the present invention, there isprovided an apparatus for providing simultaneous multiplepush-to-talk-over-cellular (PoC) multimedia service in a PoC server. Theapparatus includes a participating PoC function (PF) composer formanaging a plurality of PoC multimedia sessions; a media adapter foradjusting a size of media data received through the PF composer andtransmitted through the plurality of PoC multimedia sessions connectedto one PoC terminal; and a media transmitter for transmitting the mediadata adjusted by the media adapter to the PoC terminal.

The plurality of PoC multimedia sessions connected to one PoC terminalmay include at least one pre-established PoC multimedia session and aPoC multimedia session that is newly requested before thepre-established PoC multimedia session is terminated.

The media adapter may perform media adaptation on the media datatransmitted to the PoC terminal that supports simultaneous multiplemultimedia sessions and requests media adaptation.

The media adapter may refer to information on an auto-answer mode setupof a corresponding PoC terminal in order to check whether or not thecorresponding PoC terminal supports simultaneous multiple multimediasessions and whether the PoC terminal requests media adaptation.

The media adapter may perform query and response with a correspondingPoC terminal in order to check whether or not the corresponding PoCterminal supports simultaneous multiple multimedia sessions and whetherthe PoC terminal requests media adaptation.

According to yet another aspect of the present invention, there isprovided a system for providing simultaneous multiplepush-to-talk-over-cellular (PoC) multimedia service. The system includesa PoC terminal provided with a PoC service; and a PoC server forchecking whether the PoC terminal supports simultaneous multiplemultimedia sessions and whether the PoC terminal requests mediaadaptation when requested to establish a plurality of PoC multimediasessions of the PoC terminal, adjusting a size of media data to betransmitted to the PoC terminal through the plurality of PoC multimediasessions when the PoC terminal supports simultaneous multiple multimediasessions and requests media adaptation, and transmitting the adjustedmedia data to the PoC terminal.

The PoC terminal may include a media transmitter for exchanging packetdata with respect to the PoC server; a display controller for performingdata processing for displaying the media data received through the mediatransmitter; and a display for receiving and displaying thedisplay-processed data from the display controller.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, feature and advantages of the presentinvention will be more clearly understood from the following detaileddescription, taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 illustrates a configuration of a conventional PoC system;

FIG. 2 illustrates a schematic configuration of a conventional PoCserver;

FIG. 3 is a schematic diagram illustrating CF and PF blocks of a PoCserver;

FIG. 4 illustrates blocks of a PoC terminal and a PoC serverconstructing a system of the present invention:

FIG. 5 is a flowchart illustrating a process performed by a PoC clientfor providing simultaneous multiple PoC multimedia service in accordancewith a first embodiment of the present invention;

FIG. 6 is a flowchart illustrating a process performed by a PoC serverfor providing simultaneous multiple PoC multimedia service in accordancewith a second embodiment of the present invention;

FIG. 7 is a flow diagram of SIP-based signals between a PoC client and aPoC server in order to provide simultaneous multiple PoC multimediaservice in accordance with a third embodiment of the present invention;

FIG. 8 illustrates an example of SIP-based MBCP MIME parameters used inthe present invention;

FIG. 9 illustrates the format of an RTCP message transmitted through aPoC session in order for a PoC client to request media adaptation from aPoC server (Participating); and

FIG. 10 illustrates a parameter format and values included in SDES itemcontent and SDES items illustrated in FIG. 9.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings. Thefollowing description is illustrative of the case where the presentinvention is applied to a push-to-talk (PTT) system, particularly a PTTover cellular (PoC) system in which a PTT service is provided using amobile communication network. Generally, the PoC system makes use of aSession Initiation Protocol (SIP) and an Extended SIP in order totransmit session participation information of a group PoC call, as wellas an Extensible Mark-up Language (XML) Configuration Access Protocol(XCAP) in order to obtain information about a group. Thus, thefunctionality of the present invention to be described below can berealized by these protocols, and a basic construction of the presentinvention can be based on a PoC Rel. 1 system. Initially, an ordinaryPoC system to which the present invention can be applied will bedescribed.

FIG. 1 illustrates architecture of an ordinary PoC service system andits relevant network.

As illustrated in FIG. 1, the ordinary PoC system includes userequipment (UE) 100 acting as a PoC terminal, XML Document Management(XDM) Servers (XDMSs) 130 and 140, and a PoC server 150. The PoC systemmay further include an aggregation proxy 160. These entities may beconnected through an access network 110, a Session InitiationProtocol/Internet Protocol (SIP/IP) core 120, and a remote PoC network170.

Each of these entities will be described below in detail.

The UE 100 includes a PoC client 102, and an XDM client (XDMC) 104.

The PoC client 102 is a service requester that is built into the UE 100and performs network connection for providing a PoC service to a PoCservice subscriber while residing in the UE 100. The PoC servicesubscriber may be provided with the PoC service through the UE in whichthe PoC client is built. Hereinafter, PoC client will be used as ageneric name for a PoC terminal or a PoC service subscriber. Thus, noreference numeral is given to the PoC client, except where necessary todistinguish it particularly.

The PoC client mainly serves to establish a PoC session, participate inthe established PoC session, and terminate the established PoC sessionfrom the viewpoint of the PoC service subscriber, i.e. the PoC user. Inaddition, the PoC client acts to create and transfer a talk burst,support an instant personal alert, and perform authentication whenproviding access to the PoC service. The PoC client can be connected tothe SIP/IP core 120 that supports SIP and IP multimedia via the accessnetwork 110.

The SIP/IP core 120 is connected to the XDMSs 130 and 140 and the PoCserver 150 in order to support the PoC service. At this time, the PoCserver 150 performs a Controlling PoC Function for maintaining andmanaging the PoC session, or a Participating PoC Function forparticipating in the PoC session for a one-to-one PoC call or aone-to-many PoC call (or a group PoC call).

Meanwhile, the PoC service may accompany a service for establishing agroup session such as a conference call. To this end, the OMAspecification specifies XDMC 104 and the XDMSs 130 and 140 for a grouplist service. FIG. 1 illustrates the PoC XDMS 140 used for the PoCservice, and the shared XDMS 130 commonly used in another serviceenabler. Information about a group and its members may be input into theXDMSs 130 and 140 through the PoC client. The PoC client may be aware ofinformation about other PoC clients that can be retrieved through anindividual or group list received from the XDMSs 130 and 140.Alternatively, creating, modifying and managing the group and itsmembers with respect to the XDMSs 130 and 140 may be carried out througha communication network, such as the Internet or an Intranet, which aPoC service provider can trust. The protocols and details for the XDM,such as creating, modifying and deleting the group list, are well-knownamong those of skill in the art, and so their detailed description willbe omitted.

Further, for the purpose of the group service, the aggregation proxy 160routes a group list information request to each of the XDMSs 130 and 140according to an appropriate rule when the group list relevant request isreceived from the XDMC 104.

Next, the PoC server 150 will be described.

FIG. 2 illustrates a schematic configuration of a general PoC server.

The PoC server 150 has a Controlling PoC Function (hereinafter “CF”) forcontrolling overall maintenance and management of a PoC session, and/ora Participating PoC Function (hereinafter “PF”) for controllingmaintenance and management between each PoC session. Function-specificfeatures of the PoC server will be described with reference to Tables 1and 2. TABLE 1 Controlling PoC Function (CF) Provides centralized PoCsession handling Provides centralized Media distribution Providescentralized Talk Burst Arbitration functionality including talkeridentification Provides SIP session handling, such as SIP sessionorigination, termination, etc. Provides policy enforcement forparticipation in group sessions Provides participant informationCollects and provides centralized media quality information Providescentralized charging reports May provide transcoding between differentcodecs Supports Talk Burst Control Protocol Negotiation

As in Table 1, the PoC server performing the CF (or the Controlling PoCserver) manages a PoC session. In particular, the Controlling PoC serverreceives floor (or right-to-speak) requests from PoC clients, arrangesan order in which to give the PoC clients the floor, and gives the PoCclients the floor in that order. The Controlling PoC server alsodistributes a talk burst for which an arbitrary PoC client makes arequest, to all other PoC clients participating in a group PoC call, andprovides information of the PoC clients participating in the group PoCcall.

As in the following Table 2, the PoC server performing the PF (or theParticipating PoC server) manages PoC sessions interconnected betweenthe Controlling PoC server and each PoC client. In particular, theParticipating PoC server acts to relay the floor between the PoC clientand the Controlling PoC server when the PoC client requests the floor orwhen the Controlling PoC server gives the floor to the PoC client. Inaddition, the Participating PoC server serves to relay media between theControlling PoC server and the PoC client, perform transcoding ofdifferent codecs used between the Controlling PoC server and the PoCclient, and filter one of two concurrent PoC sessions according to thechoice of a PoC user when there is simultaneous talking in the twoconcurrent PoC sessions. TABLE 2 Participating PoC Function (PF)Provides PoC session handling May provide the Media relay functionbetween PoC client and Controlling PoC server May provide user mediaadaptation procedures May provide the Talk Burst control message relayfunction between PoC client and Controlling PoC server Provides SIPsession handling, such as SIP session origination, termination, etc, onbehalf of the represented PoC client Provides policy enforcement forincoming PoC session (e.g. access control, incoming PoC session barring,availability status, etc.) May collect and provide media qualityinformation Provides participant charging reports May provide filteringof media streams in the case of simultaneous sessions May providetranscoding between different codecs May support Talk Burst ControlProtocol Negotiation Stores the current Answer Mode and Incoming PoCSession Barring preferences of the PoC client

FIG. 3 is a schematic diagram illustrating CF and PF blocks of a PoCserver.

Referring to FIG. 3, PoC clients 102-A through 102-D provide access to aCF 300 through PFs 310-A through 310-D respectively, therebyestablishing a PoC session. Then, when the floor is granted from the CF300 to the PoC client, media based on speech of the corresponding PoCclient is transmitted to each PoC client. At this time, the PoC clientwho is granted the floor cannot appropriately speak until the PoC clientconfirms information of the other PoC clients participating in the PoCgroup session.

Meanwhile, a call processing technique for call connection in the PoCsystem allows for various procedures according to requirements andsituations of originating and terminating sides. The PoC system requiredby the OMA according to the setting of the originating and terminatingsides has the following features.

First, the terminating side can set up its own answering modes accordingto the request of a PoC client. The answering modes can be generallydivided into an auto-answer mode and a manual answer mode. In theauto-answer mode, if the terminating side is registered in an autoanswer mode user list, the terminating side can immediately send ananswer to the originating side in a corresponding network in place ofthe manual answer of a recipient. The automatic answer is sent insteadof operating the terminal in the network because the PoC server has afunction of storing the answering mode and the corresponding user listaccording to a request of the terminal to set up the answering mode. Themanual answer mode corresponds to the case where the user is notincluded in an automatic answer user list or where the answer isambiguous, and the case where the recipient sets up all users to makethe manual answer, and a PoC call request is transmitted to the user'sterminal through a terminating network and then a call is connected byacceptance of the PoC client.

Second, the PoC system is divided into two modes, an on-demand sessionmode and a pre-established (or early) session mode, according to how theconnection with a PoC server within a user's home network is set up. Thepre-established session mode is designed so that the PoC user sets up asession between a PoC client and a PoC server belonging to a PoC user'shome network in advance by PoC user's request. The pre-establishedsession is necessary to enable the PoC user to negotiate mediaparameters to be used with the PoC server in advance, and thus performrapid session establishment without renegotiating the media parametersto be used between the PoC server and client again in the future.

In order to set up the pre-established session, the PoC client providessupported media parameters to a Session Description ProtocolMultipurpose Internet Mail Extensions (SDP MIME) body through a SIPINVITE method, and responds to the media parameters provided from thePoC server. The PoC client sends, to the PoC user, identificationinformation of the pre-established session which is newly set up for aresponse message received from the PoC server, together with aconference Uniform Resource Identifier (URI).

In the case of using the pre-established session, it is possible topre-negotiate parameters such as an IP address, a port number, a codecto be used, a Talk Burst Control Protocol (TBCP) for controlling a talkburst, and so on. The on-demand session mode refers to a state in whichthe PoC user does not set up the pre-established session, and means thatthe PoC user performs a PoC call connecting procedure after receiving aninvitation message of another PoC user.

In the PoC system, the setup of the answering mode of the call requestcan be stored in the PoC server and the PoC client, the user sideterminal, which are the entities in the network.

When the answering mode is set up for the home network managing the PoCclient, the answering mode is realized in the Participating PoC server,which performs the PF within the home network to which the PoC clientbelongs.

When the answering mode is set up for the network, the Participating PoCserver automatically sends a session progress message to the callrequest network as soon as a PoC call is requested by another PoCserver. Thus, when the auto-answer mode is set up, a call requestprocedure is simplified, compared to when a session setup message istransmitted to the PoC client and then a response is made. Thus, aninitial time taken to give the floor is reduced.

However, when the auto-answer is made on the network, there is apossibility of a result not accurately reflecting a user's intentions.For this reason, the answering mode can be set up for the PoC client. Atthis time, the answering mode of the PoC client has priority over theanswering mode set up on the network. This solves a privacy problemgenerated when the answering mode is not reflected in real time due tosignal delay or error on the network when the PoC client changes its ownanswering mode and requests the PoC server to update the answering mode.

In the PoC service, the answering mode of the user can be set up for thePoC server and the PoC client, but it is determined by the PoC clientwhich reflects the user's most recent intentions. Based on thisdetermination, the stream of media (e.g. voice, image etc. of the actualuser) can be transmitted.

A procedure of establishing a PoC multimedia session in the PoC systemhaving the foregoing features will be described below.

An originating PoC client sends an INVITE message for multimedia (thatmay include various formats of audio, video and text based ondesignation of a media type), and thereby requests call processing. Inresponse to this call processing, a terminating PoC client performsvarious answering procedures based on an answering mode setup of acorresponding PoC server, and whether a pre-established session exists.The call processing procedure for a PoC call will be described withreference to procedures of the same originating and terminating sidenetworks, by way of example.

The originating PoC client sends an INVITE request message, whichincludes a SIP address of the terminating PoC client with whom theoriginating PoC client desires to communicate, to a corresponding SIP/IPcore. At this time, the INVITE request message may include elements suchas information on a PoC address of the terminating PoC client, requestedmedia parameters, information on an attribute value indicating the PoCservice, and so on. Here, the requested media parameters may includeattribute values such as an encoding method of audio and video, a rate,a payload type, etc., when a requested session is based on multimedia.

The INVITE message is transmitted to a Participating PoC server (i.e. aPF) via corresponding IP Multimedia Subsystem (IMS) servers, i.e. aProxy Call Session Control Function (P-CSCF) and a Serving Call SessionControl Function (S-CSCF), in an IMS network through a route query at aDynamic Host Configuration Protocol (DHCP) server or Domain Name System(DNS) server. Because the Participating PoC server, to which a PoC useris connected at a general call request, can be implemented as an entitydifferent from a CF (i.e. a Controlling PoC server) that manages a talkburst of an established session, the INVITE request message sent to theParticipating PoC server is delivered to the CF via an SIP/IP core ofthe corresponding network.

Meanwhile, a PoC session controlling network including the CF transmitsthe INVITE request message to a terminating side network, and thenreceives a response message from the terminating side network. The SIPresponse message received from the terminating side network may be oneof a provisional response message of 1xx, a successful response messageof 2xx, and an error response message of 4xx, 5xx or 6xx, according tothe setup of the terminating PoC client and the PF. When the auto-answermode is set up, a SIP 183 Session Progress signal is received as theresponse message. Thus, this response message allows connection betweenthe PoC server and the PoC client to be performed in the IMS network ofthe call requester. A call acceptance signal of the terminating PoCclient is sent as the SIP 183 Session Process or SIP 200 OK response andforwarded to the PoC client via the PoC servers, the CF and the PF. Whenthe SIP 200 OK or SIP 183 Session Progress signal is received from theterminating PoC server, the CF determines that a PoC call is connected,and then sends a Floor Granted signal for giving a talk burst floor tothe originating PoC client. Granting of the talk burst according to theresponse, i.e. the SIP 200 OK or SIP 183 Session Progress signal, can bedivided into two types: Confirmed and Unconfirmed. When the CF receivesthe “Unconfirmed” response, a buffering function is required.

Meanwhile, after receiving the response signal to the INVITE requestsignal, the originating PoC client A receives the Floor Granted signalforwarding a talk burst transmission enable signal (e.g. a ring backtone) using a Real-time Transport Protocol (RTP) Control Protocol(RTCP). At this time, the Floor Granted signal is generated from the CFhaving a right to arbitrate the talk burst, and transmitted to thecorresponding PoC client via the PF, which manages the corresponding PoCclient. The Floor Granted signal can be transmitted without passingthrough the SIP/IP core because of the use of a bearer's route ratherthan the SIP. Finally, the PoC user who confirms the ring back tonetransmits a media stream (e.g. voice) using Real-time Transport Protocol(RTP).

Application of the present invention to the PoC system will now bedescribed with reference to FIG. 4, which illustrates blocks of a PoCterminal and a PoC server constructing a system of the presentinvention. The system of the present invention comprises a UE 100, a PoCserver 150, and a SIP/IP core 120. Components of each of the PoC server150 and the UE 100 will be described below.

The PoC server 150 can act as a CF and PF whether or not it owns a groupsession. Herein, only a PF controlling multisessions for a multimediaPoC call will be considered. Further, the PoC server 150 can perform afunction of media adaptation. Media adaptation is for preventingoverload of the PoC network due to increased media stream transmissionby providing simultaneous multiple PoC multimedia service. Mediaadaptation functions to adapt a size of each media stream transmittedthrough the PoC session.

The PoC server 150 includes a media transmitter 420, a media adapter 430handling simultaneous multiple PoC multimedia service, and aparticipating PoC function (PF) composer 440.

The media transmitter 420 exchanges packet data and includes protocolstacks for exchanging the packet data. The media adapter 430 providessimultaneous multiple PoC multimedia service for simultaneouslytransmitting a plurality of media to a corresponding PoC client byrequest of the PoC client, and adapts a media stream size, etc. ofmultiple PoC sessions connected to the corresponding PoC client whenproviding the simultaneous multiple PoC multimedia service. Further, themedia adapter 430 outputs the adapted media data to the mediatransmitter 420. The PF composer 440 is used for supporting the multiplePoC sessions, and manages each of the multisessions. Further, the PFcomposer 440 outputs the media data received through the multiple PoCsessions 451, 452, 453 . . . to the media adapter 430.

The PoC server 150 can be connected to the PoC client through the SIP/IPcore 120 supporting SIP-based communication.

The UE 100 comprises a PoC client 102, a display 400, a displaycontroller 402, a user interface 404, and a media transmitter 410.

The PoC client 102 makes a request for provision of the simultaneousmultiple PoC multimedia service as well as media adaptation to aParticipating PoC server through a SIP or RTCP message, performs mediaadaptation on each media session through a function of the PF composer(herein, its functional blocks are not separately illustrated), andtransmits the media data to a mobile communication network. Further, thePoC client controls the display controller 402 to adjust display of acorresponding media stream and displays the received media to a user.

The display 400 outputs visual media (e.g. images, video, etc.) receivedfrom the PoC server 150. The display controller 402 performs dataprocessing for outputting the received data to the display 400. Thedisplay 400 and the display controller 402 support the multimedia. Theuser interface 404 delivers inputs of the user to the UE 100. The userinterface 404 of the present invention allows the PoC client to canchange a display type by request of the PoC user. The media transmitter410 exchanges packet data and includes IP-based network protocol stacksfor exchanging the packet data.

In the foregoing system of the present invention, the UE 100 requestsmedia adaptation based on a command of the user when the same multimediasession is requested. The PoC server 150 performs media adaptation onthe multisessions in response to the request from the UE 100, andtransmits the media data subjected to media adaptation to thecorresponding UE 100. At this time, the UE 100 can transmit to the PoCserver 150 an indicator of a corresponding media type when requestingmedia adaptation and an indicator designating the multimedia session foradapting the media type.

Meanwhile, the present invention can be realized by using SIP or RTCPmessages during the connected PoC session. The former technique can berealized by newly defining Media Burst Control Protocol (MBCP) MIMEparameters included in the SDP body part of the SIP, while the lattertechnique can be realized by defining the MBCP message transmittedthrough the RTP/RTCP channel connected after the SIP session isestablished.

Next, processes performed by the UE 100 and the PoC server 150 will bedescribed with reference to the flowchart of FIG. 5, which illustrates aprocess performed by a PoC client for providing simultaneous multiplePoC multimedia service in accordance with the present invention.

As illustrated in FIG. 5, when receiving an INVITE message of a newmultimedia PoC session (S500), the PoC client that is participating inthe pre-established PoC session determines whether it supportsmultisessions (S502). If the PoC client supports multisessions, itdetermines whether a type of media supported by the pre-established PoCsession is identical to that supported by the newly requested PoCsession. However, if the PoC client does not support multisessions, ittransmits a “Busy Here” message, a SIP “486” error response message, tothe PoC server 150 (S520).

In step S504, if the type of media supported by the pre-established PoCsession is identical to that supported by the newly requested PoCsession, the PoC client determines whether the PoC user requestssimultaneous multiple PoC multimedia service (S506). If the PoC userrequests the simultaneous multiple PoC multimedia service, the PoCclient responds to the INVITE message received in step S500 with therequest of the simultaneous multiple PoC multimedia service (S508).Further, the PoC client transmits a re-INVITE message of thepre-established PoC session, then performs media adaptation on video orimages within the pre-established session. Meanwhile, in step S504, ifthe media types supported by the two sessions are not identical, the PoCclient follows a procedure for an ordinary PoC session (S530).

If the PoC service user does not request the simultaneous multiple PoCmultimedia service, the same INVITE request as in the ordinarymultisession establishment is performed (S540).

FIG. 6 is a flowchart illustrating a process performed by a PoC serverfor providing simultaneous multiple PoC multimedia service (particularlya terminating PoC server (PF)) in accordance with another embodiment ofthe present invention.

As illustrated in FIG. 6, when receiving an INVITE message, the PoCserver 150 performs a triggering point test in which it is determinedwhether the INVITE message adopts the PoC client as a destination(S600). As a result of the triggering point test, if the destination ofthe INVITE message is not the PoC client, the PoC server re-transmitsthe INVITE message to the SIP/IP core 120 (S620).

However, if the destination of the INVITE message is the PoC client, thePoC server 150 determines whether the PoC client adopted as thedestination of the INVITE message proceeds with the session (S602). Ifthe corresponding PoC client does not proceed with the session, the PoCserver 150 establishes an ordinary PoC session for the corresponding PoCclient (S630). In step S602, if the corresponding PoC client proceedswith the session, the PoC server 150 determines whether thecorresponding PoC client supports multisessions (S604).

In steps S602 and S604, the PoC server 150 can raise a query to thecorresponding PoC client or refer to pre-stored PoC service settinginformation of the corresponding PoC client in order to determinewhether the corresponding PoC client proceeds with the session andwhether the corresponding PoC client supports multisessions. Especially,in the case in which the above-described answering mode is set up, thePoC server 150 can refer to the pre-stored information for thedetermination of steps S602 and S604. Of course, the PoC server 150 canobtain and store PoC service setting information of each PoC client inadvance even when the answering mode is not set up. The process of FIG.5 is illustrative of an embodiment corresponding to the case in whichthe PoC server 150 raises a query to the PoC client for thedetermination of steps S602 and S604.

In step S604, if the corresponding PoC client does not support themultisessions, the PoC server 150 transmits a “Busy Here” message, a SIP“486” error response message, to the terminating side of the INVITEmessage (S640). However, if the corresponding PoC client supportsmultisessions, the PoC server 150 transmits the INVITE request messageto the corresponding PoC client (S606), and receives its response. Then,the PoC server 150 receives a re-INVITE message that requests mediaadaptation on the ongoing sessions from the corresponding PoC client(S608). The PoC server 150 performs simultaneous multiple PoC multimediaservice, i.e., transmits a plurality of PoC multimedia streams, whichare subjected to media adaptation corresponding to the re-INVITE messagereceived in step S608, to the corresponding PoC client (S610).

FIG. 7 illustrates the flow of SIP-based signals between a PoC clientand a PoC server in order to provide simultaneous multiple PoCmultimedia service in accordance with the present invention.

FIG. 7 shows a case in which a PoC client A 102-A participating in onemultimedia PoC session 700 supporting audio or video is requested tojoin a new multimedia session from a PoC client C 102-C, wherein theaudio or video is managed by a PoC server X 150-X via a PoC server(Participating) A 150-A and is intended for a PoC client B 102-B.Meanwhile, the present invention can be equally applied to a case inwhich there are numerous pre-established PoC sessions. Further, FIG. 7illustrates a case in which a PoC server obtains information required todetermine whether a corresponding PoC client proceeds with the sessionand whether the corresponding PoC client supports multisessions byraising a query to the corresponding PoC client.

A PoC client A receives an INVITE message 702 requesting establishmentof a PoC session for multimedia including audio or video from a PoCclient C. The INVITE message 702 transmitted by the PoC client C istransmitted to a PoC server (Participating) A 150-A via a PoC server(Participating) C 150-C and a PoC server (Controlling) Y 150-Y which areconnected to the PoC client C. Of course, details of the INVITE message702 may vary slightly, such as routing information while passing throughthe PoC client C, the PoC server C, the PoC server Y, and the PoC serverA. Thus, details and distinguished reference numbers of the INVITEmessage 702 will be omitted because they are irrelevant to the subjectmatter of the present invention.

In the present embodiment, the PoC server A transmits the INVITE message702 to the corresponding PoC client in order make a query about whetherthe corresponding PoC client proceeds with the session and whether thecorresponding PoC client supports multisessions.

Step S704 of FIG. 7 can be considered to correspond to steps S502 andS504 of FIG. 5. The PoC client A receiving the INVITE message from thePoC server A determines whether it itself supports multisessions andwhether the pre-established PoC session and the newly requested PoCsession support the same media type (S704). The PoC client A includesthe results of step S704 in a 200 OK message 706 and transmits the 200OK message 706 to the PoC server A. The PoC server A includes a responseto whether to establish the request PoC session in the 200 OK message706 according to information received from the PoC client A, andtransmit the 200 OK message 706 to the PoC client C. The 200 OK message706 can be transmitted to the PoC client via the PoC server Y and thePoC server C. Here, the 200 OK message 706 can be assumed to be amessage accepting the corresponding session request.

When the PoC client A determines that it supports multisessions and thata user desires to be provided with the simultaneous multiple PoCmultimedia service, the PoC client A requests media adjust of theconnected multisessions (S708). This request can be transmitted to thePoC server A through a re-INVITE message 710, a SIP message. There-INVITE message 710 can include an indicator requesting mediaadaptation, a media type intended for media adaptation, a transmissionconnection direction (uplink or downlink), information about a sessionfor performing media adaptation, etc.

Meanwhile, the above-defined parameters can be included in a 200 OKresponse signal, and then transmitted so as to be compatible withstandard SIP. In step S708, the re-INVINTE message requesting the mediaadjust only with respect to a previously ongoing session 700 istransmitted. It will be easily understood that if the parameters are notincluded in the 200 OK message, the re-INVITE message as in steps S710to S712 of FIG. 7 is also transmitted with respect to the sessionestablished in steps S702 to S706.

The PoC server A receiving the re-INVITE message 710 transmits a 200 OKmessage 712 reporting that the corresponding message is received to thePoC client A.

The PoC client A performs display adaptation (S714). The displayadaptation is performed to determine how to display media streams at thePoC client A. In the present invention, the display adaptation can beused as one of the conditions of media adaptation. In other words, thePoC client A is allowed to perform media adaptation considering adisplay type. Accordingly, the PoC server A is to determine a size ofeach media stream to be transmitted to the PoC client A by reflectingthe display type determined through the display adaptation at thecorresponding PoC client A. For example, when the plurality of mediastreams are all displayed with the same size, media adaptation can beperformed so that all the media streams have the same size. On the otherhand, when the plurality of media streams are each displayed with adifferent size, media adaptation can be performed so that each of themedia streams has a size proportional to the displayed size. Inaddition, it is natural that media adaptation can be performed accordingto various conditions such as a user's choice, a pre-defined setup, etc.

In the present invention, the total size of the media streams providedto one PoC client at the same time can be determined in consideration oftransmission capacity of the PoC system. In general, the transmissioncapacity used for providing one PoC client with the simultaneousmultiple PoC multimedia service can be set to be equal to that used forproviding one PoC client with a single PoC multimedia service. This canbe easily understood from the purpose of media adaptation, which isintended to prevent an excessive load from being applied due to theprovision of the simultaneous multiple PoC multimedia service. Ofcourse, this is merely an example of an application of the presentinvention and is not intended to limit the scope of the invention.

The PoC client receiving the 200 OK message 706 transmits an ACK message718 in response to the 200 OK message 706.

The PoC client A and the PoC client B performing PoC multimediacommunication with the PoC client A through the pre-established PoCsession 700 perform setup for the simultaneous multiple PoC multimediaservice to be performed in the future by exchanging TBCP TB Taken and TBConfirmed messages 720. Thereafter, media 722 is transmitted between thePoC client A and the PoC client B based on the adaptation by theexchange of the TBCP TB Taken and TB Confirmed messages 720. Meanwhile,the PoC server A performs media adaptation on the media stream receivedfrom the PoC client B in response to the request of the PoC client A(S724). Then, the PoC server A transmits the media subjected to mediaadaptation to the PoC client A.

Further, the PoC client A and the PoC client C perform setup for thesimultaneous multiple PoC multimedia service to be performed in thefuture by exchanging TBCP TB Taken and TB Confirmed messages 728.Thereafter, media 730 is transmitted between the PoC client A and thePoC client C based on the media adaptation (S724) by the exchange of theTBCP TB Taken and TB Confirmed messages 728. Meanwhile, the PoC server Aperforms media adaptation on the media stream received from the PoCclient C in response to the request of the PoC client A (S732). Then,the PoC server A transmits the media subjected to media adaptation tothe PoC client A.

After media adaptation is performed, the PoC client A can drive adisplay suitable for the transmitted media, and receive and display themultimedia stream subjected to media adaptation at the PoC server(Participating).

The present invention has been described with reference to itsapplication to the downlink, but it can be applied to the uplink aswell. When applied to the uplink, the present invention is designed sothat one PoC client can transmit a plurality of media streams at thesame time.

As described above, the present invention can be performed through SIPor RTCP. Even when RTCP is used, a process of making a SIP response tothe INVITE message is the same as when SIP is used. However, when RTCPis used, media adaptation can be requested from the PoC client to thePoC server (Participating) by transmitting a TBCP or MBCP messagethrough an RTCP channel of independently established multisessions.Meanwhile, a procedure of performing media adaptation using the RTCPmessage can be replaced by a procedure of transmitting an RTCP messageto the established session instead of steps S710 and S712 of FIG. 7, andthus additional drawings will be omitted.

Next, the format of a message used for application of the presentinvention will be described.

First, the format of a SIP message will be described.

In the present invention, SIP-based MBCP MIME parameters can be assignedas the type illustrated in FIG. 8. Among the MBCP MIME parameters ofFIG. 8, a “TBCP” parameter value, a format value of an application mediatype introduced to support the PoC system, is additionally expanded.Here, TBCP can be converted into MBCP in order to indicate the supportof multimedia in the future. A conventional system sets parameters, suchas queue, timestamp, tb_priority, etc., as attributes of a TBCP format.In the present invention, in consideration of a transmission environmentof the multimedia multisession between the PoC server (Participating)and the PoC client, a new TBCP option parameter is proposed. The newTBCP option parameter is referred to as “mb_adapt.” However, the presentinvention is not limited by this terminology, and can be applied to allparameters having the same function regardless of the terminology used.

The present embodiment is illustrative of the case in which a fieldvalue of “mb_adapt” is set to a range of 0-4. Each field value of“mb_adapt” has a meaning as follows:

When a “mb_adapt” field is omitted or when the field value of “mb_adapt”is “0,” it means there is no request for media adaptation;

When the field value of “mb_adapt” is “1,” it means there is a requestfor media adaptation, video, and downlink;

When the field value of “mb_adapt” is “2,” it means there is a requestfor media adaptation, image, and downlink;

When the field value of “mb_adapt” is “3,” it means video and uplink;and

When the field value of “mb_adapt” is “4,” it means image and uplink.

Referring to the above-described settings of “mb_adapt,” the TBCP optionparameter value, the “mb_adapt” field value, included in the MIME bodypart is “2” in FIG. 8. Thus, it can be found that the PoC server(Participating) is requested to transmit the image stream in a downloaddirection after media adaptation.

In addition, although omitted in the embodiment, visual media caninclude “text,” and be defined as a media type of the simultaneousmultiple PoC multimedia service by expanding the “mb_adapt” fieldvalues.

The TBCP option parameter ‘mb_adapt’ is included in an SIP sessionmodification message by the PoC Client for suggestion of simultaneousmultiple reception for specific media. Accordingly, the PoC server maytransmit an ACK message including the ‘mb_adapt’ so that overlappedmedia (audio and video) are simultaneously transmitted to the PoC clientthrough a multisession. Further, the media adaptation may be performedaccording to a value of the TBCP option parameter ‘mb adapt’.

Meanwhile, the MIME parameters can be used in the SIP response messagebecause they are compatible with a general SIP function, therebyrequesting a media adaptation function. In this case, the originatingPoC server or client includes an ‘mb_adapt’ response value in the ACKmessage so that simultaneous multiple reception and media adaptation areperformed. For example, in FIG. 7, the PoC client A inserts theabove-mentioned MIME parameters into the 200 OK message 706 transmittedto the PoC server (Participating), thereby requesting media adaptationof the corresponding PoC session from the PoC server (Participating).When the SIP response signal is used, there is an advantage that nore-INVITE request is made to the corresponding session that makes aresponse.

FIG. 9 illustrates the format of an RTCP message transmitted through aPoC session in order for a PoC client to request media adaptation from aPoC server (Participating).

A first line indicates information on version, subtype, packet type,packet length, etc. A second line includes information on an address ofa PoC server (Participating) that performs media adaptation. A thirdline indicates a PoC release version. A fourth line indicates a mediaadaptation type, the following bits of which can be assigned as a zeropadding value. A fifth line indicates Source Description (SDES) itemcontent for representing information on a “PoC Session Identity” foridentifying the PoC session performing media adaptation. The SDES itemcontent may use an additional information field for future expansion.Information on an actual SIP URI for the SDES item included in the fifthline is assigned from a sixth line to the last line, thereby designatingthe PoC session for media adaptation. Each line mentioned above has asize of 32 bits.

FIG. 10 illustrates a parameter format and values included in SDES itemcontent and SDES items illustrated in FIG. 9.

A media adaptation type can have values ranging from 0 to 4 andindicates adaptation at the time of downlink/uplink of video/image.Further, SDES item content can be expressed in binary according towhether an identity of each session intended to perform the adaptationis included. For example, the SDES item content can be expressed by “1”when the target session exists and by “0” when the target session doesnot exist.

Although omitted in the embodiment, visual media may include “text,” andrequest the simultaneous multiple PoC multimedia service by expandingthe range of field values of media adaptation type of the RTCP messageto define the downlink/uplink of the text. This should be interpreted tobe included in the subject matter of the present invention.

According to the present invention as described above, multiple PoCmultimedia service can be simultaneously provided to one PoC client.Further, it is possible to reduce load on the PoC system due toincreased transmission by means of media adaptation of each of the mediastreams provided to one PoC client at the same time.

As described above, when the PoC client participating in the multimediaPoC call is requested to participate in the session including the samevideo/image media, the multimedia streams are adapted to besimultaneously transmitted and displayed from the multiple PoC sessions.Thereby, at least two video or image streams can be simultaneouslydisplayed on one terminal. Particularly, by reducing a size of the mediastream transmitted to the terminal, it is possible to improve efficiencyof wireless transmission and save cost to the PoC service user.

While the present invention has been described with reference to theexemplary embodiments, it should be understood to those skilled in theart that various other modifications and changes may be provided withinthe spirit and scope the present invention defined in the followingclaims.

1. A method for providing simultaneous multiplepush-to-talk-over-cellular (PoC) multimedia service in a PoC system, themethod comprising the steps of: receiving a request for establishment ofa new PoC multimedia session of a PoC terminal performing multimedia PoCservice through a pre-established PoC session; determining whether thePoC terminal supports simultaneous multiple multimedia sessions andwhether the PoC terminal requests media adaptation; adjusting sizes ofmultimedia data being transmitted and data to be transmitted to the PoCterminal according to whether the PoC terminal supports simultaneousmultiple multimedia sessions and whether the PoC terminal requests mediaadaptation; and transmitting the adjusted data to the PoC terminal. 2.The method according to claim 1, wherein the step of determining whetherthe PoC terminal supports simultaneous multiple multimedia sessions andwhether the PoC terminal requests media adaptation comprises:determining whether an auto-answer mode of the PoC terminal is set up;and detecting pre-stored setup information about the PoC terminal whenthe auto-answer mode is set up, and determining whether the PoC terminalsupports simultaneous multiple multimedia sessions and whether the PoCterminal requests media adaptation.
 3. The method according to claim 1,wherein the step of determining whether the PoC terminal supportssimultaneous multiple multimedia sessions and whether the PoC terminalrequests media adaptation comprises: transmitting a message queryingwhether the PoC terminal supports simultaneous multiple multimediasessions and whether the PoC terminal requests media adaptation; andreceiving a response message to the query message from the PoC terminal,detecting information included in the response message, and determiningwhether not the PoC terminal supports simultaneous multiple multimediasessions and whether the PoC terminal requests media adaptation.
 4. Themethod according to claim 3, wherein the query message and the responsemessage are transmitted using Session Initiation Protocol (SIP) orReal-time Transport Control Protocol (RTCP).
 5. The method according toclaim 1, wherein the media adaptation is carried out based on the numberof multimedia sessions that are provided at the same time.
 6. The methodaccording to claim 5, wherein the media adaptation is carried out basedon a type of requested display.
 7. The method according to claim 1,wherein the media adaptation is carried out based on a preset ruleincluding at least one of a maximum number of displays, a division ratioof display, and a screen size.
 8. The method according to claim 1,wherein the media adaptation is carried out based on a request of thePoC terminal.
 9. A message used for providing simultaneous multiplepush-to-talk-over-cellular (PoC) multimedia service, the messagecomprising a Session Initiation Protocol (SIP) message having Talk BurstControl Protocol (TBCP) option parameters indicating whether mediaadaptation is requested, whether an uplink or downlink exists, and atype of media data.
 10. An apparatus for providing simultaneous multiplepush-to-talk-over-cellular (PoC) multimedia service in a PoC server, theapparatus comprising: a participating PoC function (PF) composer formanaging a plurality of PoC multimedia sessions; a media adapter foradjusting a size of media data received through the PF composer andtransmitted through the plurality of PoC multimedia sessions connectedto one PoC terminal; and a media transmitter for transmitting the mediadata adjusted by the media adapter to the PoC terminal.
 11. Theapparatus according to claim 10, wherein the plurality of PoC multimediasessions connected to one PoC terminal include at least onepre-established PoC multimedia session and a PoC multimedia session thatis newly requested before the pre-established PoC multimedia session isterminated.
 12. The apparatus according to claim 10, wherein the mediaadapter performs media adaptation on the media data transmitted to thePoC terminal that supports simultaneous multiple multimedia sessions andrequests the media adaptation.
 13. The apparatus according to claim 12,wherein the media adapter refers to information on an auto-answer modesetup of a corresponding PoC terminal in order to determine whether thecorresponding PoC terminal supports simultaneous multiple multimediasessions and whether the PoC terminal requests media adaptation.
 14. Theapparatus according to claim 12, wherein the media adapter performsquery and response with a corresponding PoC terminal in order todetermine whether the corresponding PoC terminal supports simultaneousmultiple multimedia sessions and whether the PoC terminal requests mediaadaptation.
 15. The apparatus according to claim 14, wherein the queryand response are performed using Session Initiation Protocol (SIP) orReal-time Transport Control Protocol (RTCP).
 16. A system for providingsimultaneous multiple push-to-talk-over-cellular (PoC) multimediaservice, the system comprising: a PoC terminal provided with a PoCservice; and a PoC server for determining whether the PoC terminalsupports simultaneous multiple multimedia sessions and whether the PoCterminal requests media adaptation when requested to establish aplurality of PoC multimedia sessions of the PoC terminal, adjusting asize of media data to be transmitted to the PoC terminal through theplurality of PoC multimedia sessions when the PoC terminal supportssimultaneous multiple multimedia sessions and requests the mediaadaptation, and transmitting the adjusted media data to the PoCterminal.
 17. The system according to claim 16, further comprising aSession Initiation Protocol/Internet Protocol (SIP/IP) core providingSIP-based communication between the PoC terminal and the PoC server. 18.The system according to claim 16, wherein the PoC server comprises: aparticipating PoC function (PF) composer for managing the plurality ofPoC multimedia sessions; a media adapter for adjusting the size of mediadata received through the PF composer and transmitted through theplurality of PoC multimedia sessions connected to one PoC terminal; anda media transmitter for transmitting the media data adjusted by themedia adapter to the PoC terminal.
 19. The system according to claim 16,wherein the plurality of PoC multimedia sessions connected to one PoCterminal include at least one pre-established PoC multimedia session anda PoC multimedia session that is newly requested before thepre-established PoC multimedia session is terminated.
 20. The systemaccording to claim 16, wherein the PoC server performs media adaptationon only the media data transmitted to the PoC terminal that supportssimultaneous multiple multimedia sessions and requests media adaptation.21. The system according to claim 20, wherein the PoC server refers toinformation on an auto-answer mode setup of a corresponding PoC terminalin order to determine whether the corresponding PoC terminal supportssimultaneous multiple multimedia sessions and whether the PoC terminalrequests media adaptation.
 22. The system according to claim 20, whereinthe PoC server performs query and response with a corresponding PoCterminal in order to determine whether the corresponding PoC terminalsupports simultaneous multiple multimedia sessions and whether the PoCterminal requests media adaptation.
 23. The system according to claim22, wherein the query and response are performed using SessionInitiation Protocol (SIP) or Real-time Transport Control Protocol(RTCP).
 24. The system according to claim 16, wherein the PoC terminalcomprises: a media transmitter for exchanging packet data with respectto the PoC server; a display controller for performing data processingfor displaying the media data received through the media transmitter;and a display for receiving and displaying the display-processed datafrom the display controller.